The physical and electronic properties of aluminum nitride (AlN) give it a real potential for a wide variety of semiconductor applications. AlN has a wide energy bandgap (6.2 electron volts), high breakdown electric field and extremely high thermal conductivity. In fact, in Chow et al. Wide Bandgap Compound Semiconductors for Superior High Voltage Unipolar Power Devices(IEEE Transactions on Electron Devices, Vol. 41, No. 8, 1994) ranking of all semiconductor materials, AlN is reported to have, excluding diamond, the highest figure of merit for unipolar power device performance.
In addition, the high thermal conductivity and high optical transmissivity (i.e., low optical density) of AlN make AlN an excellent candidate substrate material. Also, AlN is likely to be the optimum substrate for the growth of pseudo-binary inter metallic compounds such as Al.sub.0.8 In.sub.0.2 N which have extremely high figures of merit for semiconductor performance (up to 4,413,000 times silicon). Although AlN has extraordinary properties for a semiconductor material and has tremendous commercial potential, AlN based semiconductor devices have been limited by the unavailability of large, low defect AlN single crystals. In their successful prior work, Slack and McNelly demonstrated a method for growing AlN single crystals via sublimation in AlN Single Crystals (Journal of Crystal Growth 42, 1977). However, the time required to grow a 12 mm by 4 mm crystal was approximately 150 hours. This growth rate is far too low to ever allow the commercial production of AlN single crystals.
In general, pulling a crystal from a molten liquid that is in equilibrium is a preferred growth process because it provides an extremely stable and uniform temperature profile across the growing crystal interface. However, despite the significant potential applications of AlN as a semiconductor material, no process has been successfully developed to pull bulk single crystals of AlN from a melt or solution of AlN that is in equilibrium, primarily because AlN only forms a liquid at extremely high pressures and temperatures and because aluminum has a very low solubility for AlN.